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[TortoiseGit.git] / src / TortoiseMerge / libsvn_diff / dirent_uri.c

/*
 * dirent_uri.c:   a library to manipulate URIs and directory entries.
 *
 * ====================================================================
 * Copyright (c) 2008-2009 CollabNet.  All rights reserved.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution.  The terms
 * are also available at http://subversion.tigris.org/license-1.html.
 * If newer versions of this license are posted there, you may use a
 * newer version instead, at your option.
 *
 * This software consists of voluntary contributions made by many
 * individuals.  For exact contribution history, see the revision
 * history and logs, available at http://subversion.tigris.org/.
 * ====================================================================
 */


\f
#include <string.h>
#include <assert.h>
#include <ctype.h>

#include <apr_uri.h>

//#include "svn_private_config.h"
#include "svn_string.h"
#include "svn_dirent_uri.h"
#include "svn_path.h"

//#include "private_uri.h"
#define SVN_PATH_LOCAL_SEPARATOR '\\'
const char *
svn_uri_canonicalize(const char *uri, apr_pool_t *pool);

/* The canonical empty path.  Can this be changed?  Well, change the empty
   test below and the path library will work, not so sure about the fs/wc
   libraries. */
#define SVN_EMPTY_PATH ""

/* TRUE if s is the canonical empty path, FALSE otherwise */
#define SVN_PATH_IS_EMPTY(s) ((s)[0] == '\0')

/* TRUE if s,n is the platform's empty path ("."), FALSE otherwise. Can
   this be changed?  Well, the path library will work, not so sure about
   the OS! */
#define SVN_PATH_IS_PLATFORM_EMPTY(s,n) ((n) == 1 && (s)[0] == '.')

/* Path type definition. Used only by internal functions. */
typedef enum {
  type_uri,
  type_dirent
} path_type_t;

\f
/**** Internal implementation functions *****/

/* Return an internal-style new path based on PATH, allocated in POOL.
 * Pass type_uri for TYPE if PATH is a uri and type_dirent if PATH
 * is a regular path.
 *
 * "Internal-style" means that separators are all '/', and the new
 * path is canonicalized.
 */
static const char *
internal_style(path_type_t type, const char *path, apr_pool_t *pool)
{
#if '/' != SVN_PATH_LOCAL_SEPARATOR
    {
      char *p = apr_pstrdup(pool, path);
      path = p;

      /* Convert all local-style separators to the canonical ones. */
      for (; *p != '\0'; ++p)
        if (*p == SVN_PATH_LOCAL_SEPARATOR)
          *p = '/';
    }
#endif

  return type == type_uri ? svn_uri_canonicalize(path, pool)
                          : svn_dirent_canonicalize(path, pool);
  /* FIXME: Should also remove trailing /.'s, if the style says so. */
}

/* Return a local-style new path based on PATH, allocated in POOL.
 * Pass type_uri for TYPE if PATH is a uri and type_dirent if PATH
 * is a regular path.
 *
 * "Local-style" means a path that looks like what users are
 * accustomed to seeing, including native separators.  The new path
 * will still be canonicalized.
 */
static const char *
local_style(path_type_t type, const char *path, apr_pool_t *pool)
{
  path = type == type_uri ? svn_uri_canonicalize(path, pool)
                          : svn_dirent_canonicalize(path, pool);
  /* FIXME: Should also remove trailing /.'s, if the style says so. */

  /* Internally, Subversion represents the current directory with the
     empty string.  But users like to see "." . */
  if (SVN_PATH_IS_EMPTY(path))
    return ".";

  /* If PATH is a URL, the "local style" is the same as the input. */
  if (type == type_uri && svn_path_is_url(path))
    return apr_pstrdup(pool, path);

#if '/' != SVN_PATH_LOCAL_SEPARATOR
    {
      char *p = apr_pstrdup(pool, path);
      path = p;

      /* Convert all canonical separators to the local-style ones. */
      for (; *p != '\0'; ++p)
        if (*p == '/')
          *p = SVN_PATH_LOCAL_SEPARATOR;
    }
#endif

  return path;
}

/* Locale insensitive tolower() for converting parts of dirents and urls
   while canonicalizing */
static char
canonicalize_to_lower(char c)
{
  if (c < 'A' || c > 'Z')
    return c;
  else
    return c - 'A' + 'a';
}
#if defined(WIN32) || defined(__CYGWIN__)
/* Locale insensitive toupper() for converting parts of dirents and urls
   while canonicalizing */
static char
canonicalize_to_upper(char c)
{
  if (c < 'a' || c > 'z')
    return c;
  else
    return c - 'a' + 'A';
}
#endif

/* Return the length of substring necessary to encompass the entire
 * previous dirent segment in DIRENT, which should be a LEN byte string.
 *
 * A trailing slash will not be included in the returned length except
 * in the case in which DIRENT is absolute and there are no more
 * previous segments.
 */
static apr_size_t
dirent_previous_segment(const char *dirent,
                        apr_size_t len)
{
  if (len == 0)
    return 0;

  --len;
  while (len > 0 && dirent[len] != '/'
#if defined(WIN32) || defined(__CYGWIN__)
                 && dirent[len] != ':'
#endif /* WIN32 or Cygwin */
        )
    --len;

  /* check if the remaining segment including trailing '/' is a root dirent */
  if (svn_dirent_is_root(dirent, len + 1))
    return len + 1;
  else
    return len;
}

/* Return the length of substring necessary to encompass the entire
 * previous uri segment in URI, which should be a LEN byte string.
 *
 * A trailing slash will not be included in the returned length except
 * in the case in which URI is absolute and there are no more
 * previous segments.
 */
static apr_size_t
uri_previous_segment(const char *uri,
                     apr_size_t len)
{
  /* ### Still the old path segment code, should start checking scheme specific format */
  if (len == 0)
    return 0;

  --len;
  while (len > 0 && uri[len] != '/')
    --len;

  /* check if the remaining segment including trailing '/' is a root dirent */
  if (svn_uri_is_root(uri, len + 1))
    return len + 1;
  else
    return len;
}

/* Return the canonicalized version of PATH, allocated in POOL.
 * Pass type_uri for TYPE if PATH is a uri and type_dirent if PATH
 * is a regular path.
 */
static const char *
canonicalize(path_type_t type, const char *path, apr_pool_t *pool)
{
  char *canon, *dst;
  const char *src;
  apr_size_t seglen;
  apr_size_t schemelen = 0;
  apr_size_t canon_segments = 0;
  svn_boolean_t url = FALSE;

  /* "" is already canonical, so just return it; note that later code
     depends on path not being zero-length.  */
  if (SVN_PATH_IS_EMPTY(path))
    return path;

  dst = canon = apr_pcalloc(pool, strlen(path) + 1);

  /* Try to parse the path as an URI. */
  url = FALSE;
  src = path;

  if (type == type_uri && *src != '/')
    {
      while (*src && (*src != '/') && (*src != ':'))
        src++;

      if (*src == ':' && *(src+1) == '/' && *(src+2) == '/')
        {
          const char *seg;

          url = TRUE;

          /* Found a scheme, convert to lowercase and copy to dst. */
          src = path;
          while (*src != ':')
            {
              *(dst++) = canonicalize_to_lower((*src++));
              schemelen++;
            }
          *(dst++) = ':';
          *(dst++) = '/';
          *(dst++) = '/';
          src += 3;
          schemelen += 3;

          /* This might be the hostname */
          seg = src;
          while (*src && (*src != '/') && (*src != '@'))
            src++;

          if (*src == '@')
            {
              /* Copy the username & password. */
              seglen = src - seg + 1;
              memcpy(dst, seg, seglen);
              dst += seglen;
              src++;
            }
          else
            src = seg;

          /* Found a hostname, convert to lowercase and copy to dst. */
          while (*src && (*src != '/'))
            *(dst++) = canonicalize_to_lower((*src++));

          /* Copy trailing slash, or null-terminator. */
          *(dst) = *(src);

          /* Move src and dst forward only if we are not
           * at null-terminator yet. */
          if (*src)
            {
              src++;
              dst++;
            }

          canon_segments = 1;
        }
    }

  if (! url)
    {
      src = path;
      /* If this is an absolute path, then just copy over the initial
         separator character. */
      if (*src == '/')
        {
          *(dst++) = *(src++);

#if defined(WIN32) || defined(__CYGWIN__)
          /* On Windows permit two leading separator characters which means an
           * UNC path. */
          if ((type == type_dirent) && *src == '/')
            *(dst++) = *(src++);
#endif /* WIN32 or Cygwin */
        }
    }

  while (*src)
    {
      /* Parse each segment, find the closing '/' */
      const char *next = src;
      while (*next && (*next != '/'))
        ++next;

      seglen = next - src;

      if (seglen == 0 || (seglen == 1 && src[0] == '.'))
        {
          /* Noop segment, so do nothing. */
        }
#if defined(WIN32) || defined(__CYGWIN__)
      /* If this is the first path segment of a file:// URI and it contains a
         windows drive letter, convert the drive letter to upper case. */
      else if (url && canon_segments == 1 && seglen == 2 &&
               (strncmp(canon, "file:", 5) == 0) &&
               src[0] >= 'a' && src[0] <= 'z' && src[1] == ':')
        {
          *(dst++) = canonicalize_to_upper(src[0]);
          *(dst++) = ':';
          if (*next)
            *(dst++) = *next;
          canon_segments++;
        }
#endif /* WIN32 or Cygwin */
      else
        {
          /* An actual segment, append it to the destination path */
          if (*next)
            seglen++;
          memcpy(dst, src, seglen);
          dst += seglen;
          canon_segments++;
        }

      /* Skip over trailing slash to the next segment. */
      src = next;
      if (*src)
        src++;
    }

  /* Remove the trailing slash if there was at least one
   * canonical segment and the last segment ends with a slash.
   *
   * But keep in mind that, for URLs, the scheme counts as a
   * canonical segment -- so if path is ONLY a scheme (such
   * as "https://") we should NOT remove the trailing slash. */
  if ((canon_segments > 0 && *(dst - 1) == '/')
      && ! (url && path[schemelen] == '\0'))
    {
      dst --;
    }

  *dst = '\0';

#if defined(WIN32) || defined(__CYGWIN__)
  /* Skip leading double slashes when there are less than 2
   * canon segments. UNC paths *MUST* have two segments. */
  if ((type == type_dirent) && canon[0] == '/' && canon[1] == '/')
    {
      if (canon_segments < 2)
        return canon + 1;
      else
        {
          /* Now we're sure this is a valid UNC path, convert the server name
             (the first path segment) to lowercase as Windows treats it as case
             insensitive.
             Note: normally the share name is treated as case insensitive too,
             but it seems to be possible to configure Samba to treat those as
             case sensitive, so better leave that alone. */
          dst = canon + 2;
          while (*dst && *dst != '/')
            *(dst++) = canonicalize_to_lower(*dst);
        }
    }
#endif /* WIN32 or Cygwin */

  return canon;
}

/* Return the string length of the longest common ancestor of PATH1 and PATH2.
 * Pass type_uri for TYPE if PATH1 and PATH2 are URIs, and type_dirent if
 * PATH1 and PATH2 are regular paths.
 *
 * If the two paths do not share a common ancestor, return 0.
 *
 * New strings are allocated in POOL.
 */
static apr_size_t
get_longest_ancestor_length(path_type_t types,
                            const char *path1,
                            const char *path2,
                            apr_pool_t *pool)
{
  apr_size_t path1_len, path2_len;
  apr_size_t i = 0;
  apr_size_t last_dirsep = 0;
#if defined(WIN32) || defined(__CYGWIN__)
  svn_boolean_t unc = FALSE;
#endif

  path1_len = strlen(path1);
  path2_len = strlen(path2);

  if (SVN_PATH_IS_EMPTY(path1) || SVN_PATH_IS_EMPTY(path2))
    return 0;

  while (path1[i] == path2[i])
    {
      /* Keep track of the last directory separator we hit. */
      if (path1[i] == '/')
        last_dirsep = i;

      i++;

      /* If we get to the end of either path, break out. */
      if ((i == path1_len) || (i == path2_len))
        break;
    }

  /* two special cases:
     1. '/' is the longest common ancestor of '/' and '/foo' */
  if (i == 1 && path1[0] == '/' && path2[0] == '/')
    return 1;
  /* 2. '' is the longest common ancestor of any non-matching
   * strings 'foo' and 'bar' */
  if (types == type_dirent && i == 0)
    return 0;

  /* Handle some windows specific cases */
#if defined(WIN32) || defined(__CYGWIN__)
  if (types == type_dirent)
    {
      /* don't count the '//' from UNC paths */
      if (last_dirsep == 1 && path1[0] == '/' && path1[1] == '/')
        {
          last_dirsep = 0;
          unc = TRUE;
        }

      /* X:/ and X:/foo */
      if (i == 3 && path1[2] == '/' && path1[1] == ':')
        return i;

      /* Cannot use SVN_ERR_ASSERT here, so we'll have to crash, sorry.
       * Note that this assertion triggers only if the code above has
       * been broken. The code below relies on this assertion, because
       * it uses [i - 1] as index. */
      assert(i > 0);

      /* X: and X:/ */
      if ((path1[i - 1] == ':' && path2[i] == '/') ||
          (path2[i - 1] == ':' && path1[i] == '/'))
          return 0;
      /* X: and X:foo */
      if (path1[i - 1] == ':' || path2[i - 1] == ':')
          return i;
    }
#endif /* WIN32 or Cygwin */

  /* last_dirsep is now the offset of the last directory separator we
     crossed before reaching a non-matching byte.  i is the offset of
     that non-matching byte, and is guaranteed to be <= the length of
     whichever path is shorter.
     If one of the paths is the common part return that. */
  if (((i == path1_len) && (path2[i] == '/'))
           || ((i == path2_len) && (path1[i] == '/'))
           || ((i == path1_len) && (i == path2_len)))
    return i;
  else
    {
      /* Nothing in common but the root folder '/' or 'X:/' for Windows
         dirents. */
#if defined(WIN32) || defined(__CYGWIN__)
      if (! unc)
        {
          /* X:/foo and X:/bar returns X:/ */
          if ((types == type_dirent) &&
              last_dirsep == 2 && path1[1] == ':' && path1[2] == '/'
                               && path2[1] == ':' && path2[2] == '/')
            return 3;
#endif
          if (last_dirsep == 0 && path1[0] == '/' && path2[0] == '/')
            return 1;
#if defined(WIN32) || defined(__CYGWIN__)
        }
#endif
    }

  return last_dirsep;
}

/* Determine whether PATH2 is a child of PATH1.
 *
 * PATH2 is a child of PATH1 if
 * 1) PATH1 is empty, and PATH2 is not empty and not an absolute path.
 * or
 * 2) PATH2 is has n components, PATH1 has x < n components,
 *    and PATH1 matches PATH2 in all its x components.
 *    Components are separated by a slash, '/'.
 *
 * Pass type_uri for TYPE if PATH1 and PATH2 are URIs, and type_dirent if
 * PATH1 and PATH2 are regular paths.
 *
 * If PATH2 is not a child of PATH1, return NULL.
 *
 * If PATH2 is a child of PATH1, and POOL is not NULL, allocate a copy
 * of the child part of PATH2 in POOL and return a pointer to the
 * newly allocated child part.
 *
 * If PATH2 is a child of PATH1, and POOL is NULL, return a pointer
 * pointing to the child part of PATH2.
 * */
static const char *
is_child(path_type_t type, const char *path1, const char *path2,
         apr_pool_t *pool)
{
  apr_size_t i;

  /* Allow "" and "foo" or "H:foo" to be parent/child */
  if (SVN_PATH_IS_EMPTY(path1))               /* "" is the parent  */
    {
      if (SVN_PATH_IS_EMPTY(path2))            /* "" not a child    */
        return NULL;

      /* check if this is an absolute path */
      if ((type == type_uri && svn_uri_is_absolute(path2)) ||
          (type == type_dirent && svn_dirent_is_absolute(path2)))
        return NULL;
      else
        /* everything else is child */
        return pool ? apr_pstrdup(pool, path2) : path2;
    }

  /* Reach the end of at least one of the paths.  How should we handle
     things like path1:"foo///bar" and path2:"foo/bar/baz"?  It doesn't
     appear to arise in the current Subversion code, it's not clear to me
     if they should be parent/child or not. */
  /* Hmmm... aren't paths assumed to be canonical in this function?
   * How can "foo///bar" even happen if the paths are canonical? */
  for (i = 0; path1[i] && path2[i]; i++)
    if (path1[i] != path2[i])
      return NULL;

  /* FIXME: This comment does not really match
   * the checks made in the code it refers to: */
  /* There are two cases that are parent/child
          ...      path1[i] == '\0'
          .../foo  path2[i] == '/'
      or
          /        path1[i] == '\0'
          /foo     path2[i] != '/'

     Other root paths (like X:/) fall under the former case:
          X:/        path1[i] == '\0'
          X:/foo     path2[i] != '/'

     Check for '//' to avoid matching '/' and '//srv'.
  */
  if (path1[i] == '\0' && path2[i])
    {
      if (path1[i - 1] == '/'
#if defined(WIN32) || defined(__CYGWIN__)
          || ((type == type_dirent) && path1[i - 1] == ':')
#endif /* WIN32 or Cygwin */
           )
        {
          if (path2[i] == '/')
            /* .../
             * ..../
             *     i   */
            return NULL;
          else
            /* .../
             * .../foo
             *     i    */
            return pool ? apr_pstrdup(pool, path2 + i) : path2 + i;
        }
      else if (path2[i] == '/')
        {
          if (path2[i + 1])
            /* ...
             * .../foo
             *    i    */
            return pool ? apr_pstrdup(pool, path2 + i + 1) : path2 + i + 1;
          else
            /* ...
             * .../
             *    i    */
            return NULL;
        }
    }

  /* Otherwise, path2 isn't a child. */
  return NULL;
}

/* FIXME: no doc string */
static svn_boolean_t
is_ancestor(path_type_t type, const char *path1, const char *path2)
{
  apr_size_t path1_len;

  /* If path1 is empty and path2 is not absolute, then path1 is an ancestor. */
  if (SVN_PATH_IS_EMPTY(path1))
    {
      return type == type_uri ? ! svn_uri_is_absolute(path2)
                              : ! svn_dirent_is_absolute(path2);
    }

  /* If path1 is a prefix of path2, then:
     - If path1 ends in a path separator,
     - If the paths are of the same length
     OR
     - path2 starts a new path component after the common prefix,
     then path1 is an ancestor. */
  path1_len = strlen(path1);
  if (strncmp(path1, path2, path1_len) == 0)
    return path1[path1_len - 1] == '/'
#if defined(WIN32) || defined(__CYGWIN__)
      || ((type == type_dirent) && path1[path1_len - 1] == ':')
#endif /* WIN32 or Cygwin */
      || (path2[path1_len] == '/' || path2[path1_len] == '\0');

  return FALSE;
}

\f
/**** Public API functions ****/

const char *
svn_dirent_internal_style(const char *dirent, apr_pool_t *pool)
{
  return internal_style(type_dirent, dirent, pool);
}

const char *
svn_dirent_local_style(const char *dirent, apr_pool_t *pool)
{
  return local_style(type_dirent, dirent, pool);
}

const char *
svn_uri_internal_style(const char *uri, apr_pool_t *pool)
{
  return internal_style(type_uri, uri, pool);
}

const char *
svn_uri_local_style(const char *uri, apr_pool_t *pool)
{
  return local_style(type_uri, uri, pool);
}

/* We decided against using apr_filepath_root here because of the negative
   performance impact (creating a pool and converting strings ). */
svn_boolean_t
svn_dirent_is_root(const char *dirent, apr_size_t len)
{
  /* directory is root if it's equal to '/' */
  if (len == 1 && dirent[0] == '/')
    return TRUE;

#if defined(WIN32) || defined(__CYGWIN__)
  /* On Windows and Cygwin, 'H:' or 'H:/' (where 'H' is any letter)
     are also root directories */
  if ((len == 2 || len == 3) &&
      (dirent[1] == ':') &&
      ((dirent[0] >= 'A' && dirent[0] <= 'Z') ||
       (dirent[0] >= 'a' && dirent[0] <= 'z')) &&
      (len == 2 || (dirent[2] == '/' && len == 3)))
    return TRUE;

  /* On Windows and Cygwin, both //drive and //server/share are root
     directories */
  if (len >= 2 && dirent[0] == '/' && dirent[1] == '/'
      && dirent[len - 1] != '/')
    {
      int segments = 0;
      int i;
      for (i = len; i >= 2; i--)
        {
          if (dirent[i] == '/')
            {
              segments ++;
              if (segments > 1)
                return FALSE;
            }
        }
      return (segments <= 1);
    }
#endif /* WIN32 or Cygwin */

  return FALSE;
}

svn_boolean_t
svn_uri_is_root(const char *uri, apr_size_t len)
{
  /* directory is root if it's equal to '/' */
  if (len == 1 && uri[0] == '/')
    return TRUE;

  return FALSE;
}

char *svn_dirent_join(const char *base,
                      const char *component,
                      apr_pool_t *pool)
{
  apr_size_t blen = strlen(base);
  apr_size_t clen = strlen(component);
  char *dirent;
  int add_separator;

  assert(svn_dirent_is_canonical(base, pool));
  assert(svn_dirent_is_canonical(component, pool));

  /* If the component is absolute, then return it.  */
  if (svn_dirent_is_absolute(component))
    return apr_pmemdup(pool, component, clen + 1);

  /* If either is empty return the other */
  if (SVN_PATH_IS_EMPTY(base))
    return apr_pmemdup(pool, component, clen + 1);
  if (SVN_PATH_IS_EMPTY(component))
    return apr_pmemdup(pool, base, blen + 1);

  /* if last character of base is already a separator, don't add a '/' */
  add_separator = 1;
  if (base[blen - 1] == '/'
#if defined(WIN32) || defined(__CYGWIN__)
       || base[blen - 1] == ':'
#endif /* WIN32 or Cygwin */
        )
          add_separator = 0;

  /* Construct the new, combined dirent. */
  dirent = apr_palloc(pool, blen + add_separator + clen + 1);
  memcpy(dirent, base, blen);
  if (add_separator)
    dirent[blen] = '/';
  memcpy(dirent + blen + add_separator, component, clen + 1);

  return dirent;
}

char *svn_dirent_join_many(apr_pool_t *pool, const char *base, ...)
{
#define MAX_SAVED_LENGTHS 10
  apr_size_t saved_lengths[MAX_SAVED_LENGTHS];
  apr_size_t total_len;
  int nargs;
  va_list va;
  const char *s;
  apr_size_t len;
  char *dirent;
  char *p;
  int add_separator;
  int base_arg = 0;

  total_len = strlen(base);

  assert(svn_dirent_is_canonical(base, pool));

  /* if last character of base is already a separator, don't add a '/' */
  add_separator = 1;
  if (total_len == 0
       || base[total_len - 1] == '/'
#if defined(WIN32) || defined(__CYGWIN__)
       || base[total_len - 1] == ':'
#endif /* WIN32 or Cygwin */
        )
          add_separator = 0;

  saved_lengths[0] = total_len;

  /* Compute the length of the resulting string. */

  nargs = 0;
  va_start(va, base);
  while ((s = va_arg(va, const char *)) != NULL)
    {
      len = strlen(s);

      assert(svn_dirent_is_canonical(s, pool));

      if (SVN_PATH_IS_EMPTY(s))
        continue;

      if (nargs++ < MAX_SAVED_LENGTHS)
        saved_lengths[nargs] = len;

      if (svn_dirent_is_absolute(s))
        {
          /* an absolute dirent. skip all components to this point and reset
             the total length. */
          total_len = len;
          base_arg = nargs;
          add_separator = 1;
          if (s[len - 1] == '/'
        #if defined(WIN32) || defined(__CYGWIN__)
               || s[len - 1] == ':'
        #endif /* WIN32 or Cygwin */
                )
                  add_separator = 0;
        }
      else if (nargs == base_arg + 1)
        {
          total_len += add_separator + len;
        }
      else
        {
          total_len += 1 + len;
        }
    }
  va_end(va);

  /* base == "/" and no further components. just return that. */
  if (add_separator == 0 && total_len == 1)
    return apr_pmemdup(pool, "/", 2);

  /* we got the total size. allocate it, with room for a NULL character. */
  dirent = p = apr_palloc(pool, total_len + 1);

  /* if we aren't supposed to skip forward to an absolute component, and if
     this is not an empty base that we are skipping, then copy the base
     into the output. */
  if (base_arg == 0 && ! (SVN_PATH_IS_EMPTY(base)))
    {
      if (SVN_PATH_IS_EMPTY(base))
        memcpy(p, SVN_EMPTY_PATH, len = saved_lengths[0]);
      else
        memcpy(p, base, len = saved_lengths[0]);
      p += len;
    }

  nargs = 0;
  va_start(va, base);
  while ((s = va_arg(va, const char *)) != NULL)
    {
      if (SVN_PATH_IS_EMPTY(s))
        continue;

      if (++nargs < base_arg)
        continue;

      if (nargs < MAX_SAVED_LENGTHS)
        len = saved_lengths[nargs];
      else
        len = strlen(s);

      /* insert a separator if we aren't copying in the first component
         (which can happen when base_arg is set). also, don't put in a slash
         if the prior character is a slash (occurs when prior component
         is "/"). */
      if (p != dirent &&
          ( ! (nargs - 1 == base_arg) || add_separator))
        *p++ = '/';

      /* copy the new component and advance the pointer */
      memcpy(p, s, len);
      p += len;
    }
  va_end(va);

  *p = '\0';
  assert((apr_size_t)(p - dirent) == total_len);

  return dirent;
}

char *
svn_dirent_dirname(const char *dirent, apr_pool_t *pool)
{
  apr_size_t len = strlen(dirent);

  assert(svn_dirent_is_canonical(dirent, pool));

  if (svn_dirent_is_root(dirent, len))
    return apr_pstrmemdup(pool, dirent, len);
  else
    return apr_pstrmemdup(pool, dirent, dirent_previous_segment(dirent, len));
}

char *
svn_uri_dirname(const char *uri, apr_pool_t *pool)
{
  apr_size_t len = strlen(uri);

  assert(svn_uri_is_canonical(uri, pool));

  if (svn_uri_is_root(uri, len))
    return apr_pstrmemdup(pool, uri, len);
  else
    return apr_pstrmemdup(pool, uri, uri_previous_segment(uri, len));
}

char *
svn_dirent_get_longest_ancestor(const char *dirent1,
                                const char *dirent2,
                                apr_pool_t *pool)
{
  return apr_pstrndup(pool, dirent1,
                      get_longest_ancestor_length(type_dirent, dirent1,
                                                  dirent2, pool));
}

char *
svn_uri_get_longest_ancestor(const char *uri1,
                             const char *uri2,
                             apr_pool_t *pool)
{
  svn_boolean_t uri1_is_url, uri2_is_url;
  uri1_is_url = svn_path_is_url(uri1);
  uri2_is_url = svn_path_is_url(uri2);

  if (uri1_is_url && uri2_is_url)
    {
      apr_size_t uri_ancestor_len;
      apr_size_t i = 0;

      /* Find ':' */
      while (1)
        {
          /* No shared protocol => no common prefix */
          if (uri1[i] != uri2[i])
            return apr_pmemdup(pool, SVN_EMPTY_PATH,
                               sizeof(SVN_EMPTY_PATH));

          if (uri1[i] == ':')
            break;

          /* They're both URLs, so EOS can't come before ':' */
          assert((uri1[i] != '\0') && (uri2[i] != '\0'));

          i++;
        }

      i += 3;  /* Advance past '://' */

      uri_ancestor_len = get_longest_ancestor_length(type_uri, uri1 + i,
                                                     uri2 + i, pool);

      if (uri_ancestor_len == 0 ||
          (uri_ancestor_len == 1 && (uri1 + i)[0] == '/'))
        return apr_pmemdup(pool, SVN_EMPTY_PATH, sizeof(SVN_EMPTY_PATH));
      else
        return apr_pstrndup(pool, uri1, uri_ancestor_len + i);
    }

  else if ((! uri1_is_url) && (! uri2_is_url))
    {
      return apr_pstrndup(pool, uri1,
                          get_longest_ancestor_length(type_uri, uri1, uri2,
                                                      pool));
    }

  else
    {
      /* A URL and a non-URL => no common prefix */
      return apr_pmemdup(pool, SVN_EMPTY_PATH, sizeof(SVN_EMPTY_PATH));
    }
}

const char *
svn_dirent_is_child(const char *dirent1,
                    const char *dirent2,
                    apr_pool_t *pool)
{
  return is_child(type_dirent, dirent1, dirent2, pool);
}

const char *
svn_uri_is_child(const char *uri1,
                 const char *uri2,
                 apr_pool_t *pool)
{
  return is_child(type_uri, uri1, uri2, pool);
}

svn_boolean_t
svn_dirent_is_ancestor(const char *dirent1, const char *dirent2)
{
  return is_ancestor(type_dirent, dirent1, dirent2);
}

svn_boolean_t
svn_uri_is_ancestor(const char *uri1, const char *uri2)
{
  return is_ancestor(type_uri, uri1, uri2);
}

svn_boolean_t
svn_dirent_is_absolute(const char *dirent)
{
  if (! dirent)
    return FALSE;

  /* dirent is absolute if it starts with '/' */
  if (dirent[0] == '/')
    return TRUE;

  /* On Windows, dirent is also absolute when it starts with 'H:' or 'H:/'
     where 'H' is any letter. */
#if defined(WIN32) || defined(__CYGWIN__)
  if (((dirent[0] >= 'A' && dirent[0] <= 'Z') ||
       (dirent[0] >= 'a' && dirent[0] <= 'z')) &&
      (dirent[1] == ':'))
     return TRUE;
#endif /* WIN32 or Cygwin */

  return FALSE;
}

svn_boolean_t
svn_uri_is_absolute(const char *uri)
{
  /* uri is absolute if it starts with '/' */
  if (uri && uri[0] == '/')
    return TRUE;

  /* URLs are absolute. */
  return svn_path_is_url(uri);
}

svn_error_t *
svn_dirent_get_absolute(const char **pabsolute,
                        const char *relative,
                        apr_pool_t *pool)
{
  char *buffer;
  apr_status_t apr_err;
  const char *path_apr;

  /* Merge the current working directory with the relative dirent. */
  SVN_ERR(svn_path_cstring_from_utf8(&path_apr, relative, pool));

  apr_err = apr_filepath_merge(&buffer, NULL,
                               path_apr,
                               APR_FILEPATH_NOTRELATIVE,
                               pool);
  if (apr_err)
    return svn_error_createf(SVN_ERR_BAD_FILENAME, NULL,
                             _("Couldn't determine absolute path of '%s'"),
                             svn_path_local_style(relative, pool));

  SVN_ERR(svn_path_cstring_to_utf8(pabsolute, buffer, pool));
  *pabsolute = svn_dirent_canonicalize(*pabsolute, pool);
  return SVN_NO_ERROR;
}

const char *
svn_uri_canonicalize(const char *uri, apr_pool_t *pool)
{
  return canonicalize(type_uri, uri, pool);;
}

const char *
svn_dirent_canonicalize(const char *dirent, apr_pool_t *pool)
{
  const char *dst = canonicalize(type_dirent, dirent, pool);;

#if defined(WIN32) || defined(__CYGWIN__)
  /* Handle a specific case on Windows where path == "X:/". Here we have to
     append the final '/', as svn_path_canonicalize will chop this of. */
  if (((dirent[0] >= 'A' && dirent[0] <= 'Z') ||
        (dirent[0] >= 'a' && dirent[0] <= 'z')) &&
        dirent[1] == ':' && dirent[2] == '/' &&
        dst[3] == '\0')
    {
      char *dst_slash = apr_pcalloc(pool, 4);
      dst_slash[0] =  dirent[0];
      dst_slash[1] = ':';
      dst_slash[2] = '/';
      dst_slash[3] = '\0';

      return dst_slash;
    }
#endif /* WIN32 or Cygwin */

  return dst;
}

svn_boolean_t
svn_dirent_is_canonical(const char *dirent, apr_pool_t *pool)
{
  return (strcmp(dirent, svn_dirent_canonicalize(dirent, pool)) == 0);
}

svn_boolean_t
svn_uri_is_canonical(const char *uri, apr_pool_t *pool)
{
  const char *ptr = uri, *seg = uri;

  /* URI is canonical if it has:
   *  - no '.' segments
   *  - no closing '/', unless for the root path '/' itself
   *  - no '//'
   *  - lowercase URL scheme
   *  - lowercase URL hostname
   */

  if (*uri == '\0')
    return TRUE;

  /* Maybe parse hostname and scheme. */
  if (*ptr != '/')
    {
      while (*ptr && (*ptr != '/') && (*ptr != ':'))
        ptr++;

      if (*ptr == ':' && *(ptr+1) == '/' && *(ptr+2) == '/')
        {
          /* Found a scheme, check that it's all lowercase. */
          ptr = uri;
          while (*ptr != ':')
            {
              if (*ptr >= 'A' && *ptr <= 'Z')
                return FALSE;
              ptr++;
            }
          /* Skip :// */
          ptr += 3;

          /* This might be the hostname */
          seg = ptr;
          while (*ptr && (*ptr != '/') && (*ptr != '@'))
            ptr++;

          if (! *ptr)
            return TRUE;

          if (*ptr == '@')
            seg = ptr + 1;

          /* Found a hostname, check that it's all lowercase. */
          ptr = seg;
          while (*ptr && *ptr != '/')
            {
              if (*ptr >= 'A' && *ptr <= 'Z')
                return FALSE;
              ptr++;
            }
        }
      else
        {
          /* Didn't find a scheme; finish the segment. */
          while (*ptr && *ptr != '/')
            ptr++;
        }
    }

#if defined(WIN32) || defined(__CYGWIN__)
  if (*ptr == '/')
    {
      /* If this is a file url, ptr now points to the third '/' in
         file:///C:/path. Check that if we have such a URL the drive
         letter is in uppercase. */
      if (strncmp(uri, "file:", 5) == 0 &&
          ! (*(ptr+1) >= 'A' && *(ptr+1) <= 'Z') &&
          *(ptr+2) == ':')
        return FALSE;
    }
#endif /* WIN32 or Cygwin */

  /* Now validate the rest of the URI. */
  while(1)
    {
      int seglen = ptr - seg;

      if (seglen == 1 && *seg == '.')
        return FALSE;  /*  /./   */

      if (*ptr == '/' && *(ptr+1) == '/')
        return FALSE;  /*  //    */

      if (! *ptr && *(ptr - 1) == '/' && ptr - 1 != uri)
        return FALSE;  /* foo/  */

      if (! *ptr)
        break;

      if (*ptr == '/')
        ptr++;
      seg = ptr;

      while (*ptr && (*ptr != '/'))
        ptr++;
    }

  return TRUE;
}